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“Click” Synthesis of Heteroleptic Tris-Cyclometalated Iridium(III) Complexes: Cu(I) Triazolide Intermediates as Transmetalating Reagents

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journal contribution
posted on 15.08.2011, 00:00 by Shuang Liu, Peter Müller, Michael K. Takase, Timothy M. Swager
Efficient synthesis of heteroleptic tris-cyclometalated Ir(III) complexes mer-Ir(C/\N)2(trpy) (trpy = 2-(1H-[1,2,3]triazol-4-yl)pyridine) is achieved by using the Cu(I)-triazolide intermediates formed in “click” reactions as transmetalating reagents. Ligand preparation and cyclometalation of Ir(III) is accomplished in one pot. The robust nature of click chemistry provides opportunities to introduce different functional groups to the cyclometalated system, for example, alkyl, perfluoroalkyl, and aryl moieties. All of the meridional isomers show short-lived phosphorescence at room temperature, both in solution and in the solid state. DFT calculations indicates that the phosphorescence of mer-Ir(C/\N)2(trpy) is attributed to the 3MLCT and 3LC mixed excited states, also supported by the broad spectral shape and hypsochromic shift upon media rigidification. The luminescence efficiency and excited state lifetimes of the cyclometalated complexes can be tuned by varying the substituents on the triazole ring, while the emission color is mainly determined by the phenylpyridine-based ligands. Moreover, the trpy ligand can acquire the N/\N chelating mode under selective reaction conditions. mer-Ir(C/\N)2(trpy) complexes isomerize into cationic [Ir(C/\N)2(N/\N_trpy)]+ species instead of their fac isomers upon heating or UV radiation. This can be explained by the strong trans influence exerted by the phenyl groups. The weakened Ir–C(trpy) bonds are likely to be activated and protonated, leading to the switch of the trpy ligand to a thermodynamically more stable N/\N chelating mode.